Positive displacement compressors



June 14, 1966 K. B. NORLIN ETAL 3,255,954

POSITIVE DISPLACEMENT COMPRESSORS 2 Sheets-Sheet 1 Filed July 6, 1962 I l l I Fig! ii k 3 80 6/ \3 4 J 7 3 EW 2 x 2 m F 5 6 7 32 Q 2 June 14, 1966 NQRLlN ETAL 3,255,954

POSITIVE DISPLACEMENT COMPRESSORS Filed July 6, 1962 2 Sheets-Sheet 2 Fig.3

INVENTORS United States Patent s,255,a54 POSITIVE DESPLACEMENT COMPRESSORS Knut Bertil Norlin, Nacka, Sweden, and Iwan Ernst Roland Alrerman, Antwerp, Belgium, assignors to Atlas Copco Aktiebolag, Nacka, Sweden, a corporation of Sweden Filed July 6, 1962, Ser. No. 207,874 (llairns. (Cl. 230--31) This invention relates to positive displacement compressors. Such compressors may be single or multistage reciprocating compressors or single or multi-stage rotary vane or screw compressors or other positive displacement compressors in compressors having automatic valves, which is usual in reciprocating compressors, said check valve may be the delivery valve or valves in the V compressor, or a separate valve in the delivery conduit.

One object of the invention is to provide an unloading mechanism for compressors of the above type which permits the compressor to be unloaded and to run idle with substantially the same pressure in the intake passage and said compression chamber in the compressor, which preferably is the high pressure compression chamber in a two or multiple stage compressor; thus the compressor can run unloaded with substantially the same body of gaseous fluid circulating through the compressor during the unloading period. A still further object of the invention is to provide a compressor in which moisture or impurities do not accumulate in the compressor during unloading periods. which does not blow out a wet intake air filter during the unloading period. A still further object of the invention is to provide a compressor in which the temperature of the gaseous fluid circulated through the compressor during idling periods is maintained at a low value. A still fiurther object of the invention is to provide an unloading mechanism which is inexpensive and safe in operation and which does not affect the suction and outlet valves of the compressor. Another object of the invention is to avoid oil deposits around the compressor during idling, and to prevent disturbing noise of the idle running compressor.

In the accompanying drawings one embodiment of a compressor according to the invention is illustrated by way of example. FIG. 1 is a side view and partial vertical section of a two-stage, two-cylinder reciprocating compressor according to the invention. FIG. 1a is an enlarged broken away detail of the compressor in FIG. 1. FIG. 2 is a section showing the unloading valve mechanism according to the invention on a larger scale. FIG. 3 is a modification involving an intake throttle valve arranged at the intake of the low pressure cylinder of a compressor similar to FIG. 1.

The compressor illustrated in FIGS. 1-2 is an air cooled two-cylinder, two-stage compressor which may be driven by an internal combustion engine or in any suitable way. The compressor consists of a casing 1 carrying two cylinders 2 and 3 for low and high pressure compression. The low pressure cylinder has a cylinder head 4 which through an intake manifold 5 is connected to an air intake filter 6 through which air is conveyed to the low pressure cylinder. The cylinder head 4 is provided with an admission valve assembly 7 and a pressure valve assembly 8 provided in inlet and outlet chambers 9 and 10, respectively, the latter communicating through a conduit 11 forming an air cooled intermediate cooler with an admission valve chamber 12 provided in a cylinder head 13 carried by the high pressure cylinder 3. The cylinder head 13 is also provided with a delivery chamber 14 from which a conduit 15 carries compressed air to a receiver 16. 17 and 18 indicate the suction and pressure valve assemblies of the high pressure cylinder.

There is also provided a compressor 20 and 21 indicate the low and high pressure pistons which by means of piston rods 22, 23 may be connected to a crank shaft 24 driven by the internal combustion engine or otherwise through a suitable, not illustrated coupling. An unloading valve 25 is provided in a bore in the cylinder head 13 of the high pressure cylinder 3. Said unloading valve 25 consists of a large piston portion (see FIG. 2) 26 and a small piston portion 27 provided on a stem 28 which carries the unloading valve member 29 at one end. The small piston portion 27 is movable in a bore 30 and the large piston portion 26 in a bore 31 in the cylinder head 13. The

bore 30 communicates with the compression chamber 32 of the high pressure working cylinder through a tapering bore 33 forming a seat for the unloading valve member 29 at the juncture between the bore 30 and the compression chamber 32. A helical spring 34 which is carried in a bore 35 in a spring'retaining and adjustment plug 36 acts on the large piston portion 26 and normally keeps the valve member 29 seated on the seat 33 against any compression pressure which may occur during operation in the compression chamber 32. An annular space 37 formed around the stem 28 between the large piston portion 26 and the small piston portion 27 communicates through a bore 38 and a pipe 39 with a pressure regulating valve 40 provided on or connected to the air receiver 16 through a pipe 70. The valve 40 may be of conventional design and will be described hereinbelow. An annular space 41 formed around the stem 28 between the small piston portion 27 and the seat 33 communicates through a bore 42 and a pipe 43 with the intake manifold 5 connecting the air filter 6 to the inlet valve chamber 9 of the low pressure cylinder 2. 44 is the delivery pipe from the receiver 16 to the compressed air consuming tools or apparatus.

The regulating valve 49, FIG. la, is connected to the air receiver 16 through the connection 71 and pipe 70. Through a connection 72 and pipe 39 it communicates with the unloading valve 25 in the cylinder head 13.

The actual regulating member consists of a springloaded valve member 73, which in its lower position seals against a valve seat 74 and, in its upper position, against a valve seat 75. During compression periods of the compressor, the valve member remains in its lower position. The tension of a spring 76 acting on a valve stem and spring guide 77 is then sufilcient to overcome the airpressure on the bottom of the valve member 73. The connection 72 to the unloading valve communicates wit-h the atmosphere through the passage around the valve stem 77 and an air vent hole 78 in an adjusting screw 79.

When the pressure in the air receiver 16 and thus under the valve member 73 reaches a predetermined value, the tension of the spring 76 is overcome and the valve member is lifted to its upper position. When this occurs, the unloading valve 25 is operated since venting to the atmosphere is interrupted and pipe 39 is put into communication with the air receiver 16 through the fine passage between the valve member 73 and a bore 81 in the valve housing 80. Consequently, the unloading valve is actuated by compressed air acting on the large underside of the piston portion 26, resulting in the valve member 29 being opened, and held open, so that the compressor idles.

When the pressure in the air receiver drops to a predetermined value, the valve member 73 resumes its lower position due to the tension of the spring 76. The unloading valve 25 is now put into communication with the atmosphere through pipe 39 and vent passage 78 and the compressor is reloaded. The diiference between the unloading pressure and the reloading pressure is determined by the stroke of the valve member 73 and may be adjusted by means of brass shims 82 of various thickness provided between the housing 80 and the connection 7 1 and a bushing 83.

The unloading mechanism described in connection with FIGS. l2 operates in the following manner:

It may be assumed that at first the compressor is at stand-still and the receiver 16 notloaded. It is then assumed that the compressor is started and begins to deliver air to the receiver 16 in which air pressure is slowly building up. The unloading valve 29 is closed during this operation since at the start the compressor anyway operates substantially without resistance. When the compressor has gained speed the pressure in the receiver 16 rises and, if no air is drawn from the receiver to a consumer, the air pressure in the receiver will rise to the maximum pressure for which the pressure regulating valve 40 is set. When said pressure is reached the valve 40 opens and maximum receiver pressure is admitted through the pipe 39 to the annular space 37 and the underside of the large piston 26 which is displaced against the action of the helical spring 34 so that the valve 29 is opened. The valve 29 then opens the passage from the compression chamber 32 through the annular space 41, the bore 42 and pipe 43 to the intake manifold 5, so that the compressor is unloaded. The delivery valve 18 or a separate check valve 19 or both prevent the compressed air in the receiver 16 from escaping back to the compression chamber 32 and the high pressure cylinder.

During the unloading or idling period the low pressure piston delivers air to the intermediate cooler 11 and the high pressure cylinder which air is then without sub stantial compression returned through the pipe 43 to the air intake manifold and the inlet chamber 9 of the low pressure cylinder. Consequently, said air is circulated through the compressor the intermediate cooler and the pipe 43 substantially at admission chamber pressure and substantially no new air is drawn into this circuit through the air filter 6 as long as the compressor is idling, so that no new moisture or impurities will collect in this circuit. Due to the effect of the intermediate cooler the temperature of the circulating air is kept at a very low value.

In the modification of the invention illustrated in FIG. 3 a throttle valve 45 is movable in a housing 46 arranged between the air intake filter 6 and the intake manifold 5. The pipe 43 from the unloading valve is connected to an inlet chamber 47 in the housing between the filter 6 and the throttle valve 45. An outlet chamber 48 in the housing 46 communicates with the intake manifold 5.

The valve member 45 is operated by compressed air supplied through a pipe 49 which may be branched off from the pipe 3-9 so that the valve member 45 is actuated simultaneously with the valve member 29 against the action of a spring 50. The pipe 49 communicates with a chamber 51 which piston '52 formed on the stem 53 of the valve 45 is movable.

The throttling of the intake to the inlet chamber 9 during idling of the compressor produces considerable vacuum in the inlet chamber 9 and, consequently, in this embodiment a very reduced air quantity is circulated through the unloading valve 25 and the pipe 43 which makes it possible to reduce the dimensions of these parts correspondingly and also reduces energy consumption during idle running of the compressor. The throttle valve also serves to eliminate heavy back flow through the in take filter which may cause blow out of the oil in case of oil bath filters.

The embodiment of the invention above described and illustrated in the drawings should only be considered as an example and the invention may be modified in several diflerent ways within the scope of the following claims.

What we claim is:

1. In a positive displacement compressor apparatus of the character described having a low pressure stage and a stage with a working cylinder disposed therein for positively compressing a gaseous fluid, a passage leading from said low pressure stage to said high pressure stage, an admission chamber in said low pressure stage, an intake passage leading to said admission chamber for admitting gaseous fluid for compression, and a receiver for receiving said compressed gaseous fluid, the combination which comprises conduit means connected to said high pressure stage and said receiver for conveying said compressed gaseous fluid from said high pressure stage to said receiver, a check valve in said conduit means preventing flow of said compressed gaseous fluid from said receiver to said high pressure stage, pipe means leading directly from said high pressure stage to said intake passage, valve means in said pipe means and connected to said receiver for normally closing said pipe means, said valve means being responsive to a predetermined pressure in said receiver for opening said pipe means thereby allowing direct flow from said high pressure stage to said intake passage causing flow through all of said pipe means and said intake passage and said admission chamber and said high and low pressure stages of susbtantially the same said gaseous fluid during the time when said receiver is at said predetermined pressure.

2. Apparatus as recited in claim 1 in which cooling means are provided around said passage leading from said low pressure stage to said high pressure for cooling the said compressed gaseous fluid flowing therein.

3. In a positive displacement compressor apparatus of the character described having a working cylinder disposed therein for positively compressing a gaseous fluid, an admission chamber and intake passage leading to said admission chamber for admitting gaseous fluid for compression and a receiver for receiving said compressed gaseous fluid, the combination which comprises conduit means connected to said cylinder and said receiver for conveying said compressed gaseous fluid from said cylinder to said receiver, a check valve in said conduit means preventing flow of said compressed gaseous fluid from said receiver to said cylinder, pipe means leading directly from said cylinder to said intake passage, valve means in said pipe means and in flow communication with said receiver for normally closing said pipe means, said valve means being responsive to a predetermined pressure in said receiver for opening said pipe means thereby allowing flow directly from said cylinder to said intake passage caus-.

ing flow through said pipe means, said intake passage, said admission chamber, and said cylinder of substantially the same said gaseous fluid during the time when said receiver is at said predetermined pressure, a throttle valve in said intake passage, and means connected to said conduit means for moving said throttle valve to a throttling position for diminishing the quantity of gaseous fluid flowing through said intake passage upon said receiver attaining said predetermined pressure, said pipe means being attached to said intake passage upstream of said throttle valve.

4. In a positive displacement compressor apparatus of the character described having a working cylinder disposed therein for positively compressing a gaseous fluid, an admission chamber and an intake passage leading to said admission chamber for admitting gaseous fluid for compression, a receiver for receiving said compressed gaseous fluid, conduit means connected to said cylinder and said receiver for conveying said compressed gaseous fluid from said cylinder to said receiver, the combination which comprises a check valve in said conduit means preventing flow of said compressed gaseous fluid from said receiver to said cylinder, pipe means leading directly from said cylinder to said intake passage, and valve means in said pipe means and in flow communication with said receiver for permitting flow of said gaseous fluid directly from said cylinder to said intake passage when said valve means is open, said valve means including a valve casing in flow communication with said compression chamber, a multiple diameter bore in said valve casing, a valve member comprising a stem, a large piston at one end of said stem, a valve body at the end of said stem opposite said large piston with a small piston disposed intermediate thereof, an annular space surrounding said valve stem between said large and small pistons in said bore, a pressure-responsive communication means between said annular space and said receiver for supplying pressure fluid to said space to operate said valve member upon attainment of a predetermined pressure in said receiver, spring means in said valve casing and disposed against said stem for holding said valve body closed against flow communication with said compression chamber, said pressure fluid from said receiver acting upon said large piston to move said valve stem and said valve body against said spring means for opening said flow communication between said compression chamber and said pipe means upon said receiver attaining said predetermined pressure.

5. In a positive displacement compressor apparatus of the character described having a low pressure stage and a Working cylinder disposed therein and a high pressure stage with a Working cylinder disposed therein for positively compressing a gaseous fluid, a passage leading from said low pressure stage to said high pressure stage, an admission chamber in said low pressure stage, an admission chamber in said high pressure stage, and an intake passage leading to said admission chamber in said low pressure stage for admitting gaseous fluid for compression and a receiver for receiving said compressed gaseous fluid, the combination which comprises conduit means connected to said high pressure stage and said receiver for conveying said compressed gaseous fluid from said high pressure stage to said receiver, a check valve in said conduit means preventing flow of said compressed gaseous fluid from said receiver to said high pressure stage, valve means in said high pressure stage and in flow communication with said cylinder thereof and separate from said high pressure stage admission chamber in direct flow communication with said intake passage, and pipe means connected to said valve means providing flow communication with said receiver, said valve means being responsive to a predetermined pressure in said receiver for opening a direct communication between said cylinder of said high pressure stage and said intake passage to allow gaseous fluid to flow directly from said high pressure stage cylinder to unload said compressor for reducing the power consumption of said compressor during idling periods.

References Cited by the Examiner UNITED STATES PATENTS 685,704 10/1901 Wilkinson 230-22 953,617 3/1910 Herr 230-26 1,176,998 3/1916 Ward et a1. 230-26 1,211,074 1/1917 Bulkley 230-26 1,240,539 9/1917 Bulkley 230-26 1,625,780 4/1927 Atkins 251-63 2,042,085 5/ 1936 Aikman 230-26 2,415,060 1/1947 Craig 230-22 2,726,032 12/1955 Cooper et a1. 230-2-2 2,856,121 10/1958 Buehler 230-22 2,928,646 3/1960 Ashbrook 251-63 2,984,404 5/1961 Klein 230-22 3,022,040 2/ 1962 Miller 251-63 3,076,593 2/1963 Newton 230-22 LAURENCE V. EFNER, Primary Examiner.

' G. M. THOMAS, Assistant Examiner. 

1. IN A POSITIVE DISPLACEMENT COMPRESSOR APPARATUS OF THE CHARACTER DESCRIBED HAVING A LOW PRESSURE STAGE AND A WORKING CYLINDER DISPOSED THEREIN AND A HIGH PRESSURE STAGE WITH A WORKING CYLINDER DISPOSED THEREIN FOR POSITIVELY COMPRESSING A GASEOUS FLUID, A PASSAGE LEADING FROM SAID LOW PRESSURE STAGE TO SAID HIGH PRESSURE STAGE, AN ADMISSION CHAMBER IN SAID LOW PRESSURE STAGE, AN INTAKE PASSAGE LEADING TO SAID ADMISSION CHAMBER FOR ADMITTING GASEOUS FLUID FOR COMPRESSION, AND A RECEIVER FOR RECEIVING SAID COMPRESSED GASEOUS FLUID, THE COMBINATION WHICH COMPRISES CONDUIT MEANS CONNECTED TO SAD HIGH PRESSURE STAGE AND SAID RECEIVER FOR CONVEYING SAID COMPRESSED GASEOUS FLUID FROM SAID HIGH PRESSURE STAGE TO SAID RECEIVER, A CHECK VALVE IN SAID CONDUIT MEANS PREVENTING FLOW OF SAID COMPRESSED GASEOUS FLUID FROM 